My understanding of the Redfield Ratio & it’s relation to algae growth. Am I correct?

[FrugalReefer]

This is how I understand the Redfield Ratio with regards to nitrates and phosphates and how it relates to creating conditions for algae growth. Please chime in and let me know if my thinking is correct.

If phosphates are high and nitrates are low, the low nitrates will limit the amount of phosphates being taken up by marine organisms (16:1 N to P) which will result in phosphates slowly building up in the water column over time. According to the chart, this favors an environment favorable for blue green algae and cyano.

If nitrates are high and phosphates are low, the low phosphates will limit the amount of nitrates being taken up by marine organisms (16:1 N to P) which will result in nitrates slowly building up in the water column over time. According to the chart, this favors an environment favorable for green algae and diatoms also I believe.

Correct right? This confuses me somewhat because we have always been taught in this hobby, and freshwater for that matter, that high phosphates are the reason for algae growing in your tank, mainly stuff like GHA, bryopsis and what not. Yet if my view of the Redfield Ratio is correct, it works the other way around, with excess nitrates more likely to fuel green algae while excess phosphates are more related to cyano.

Also, if this is how algae growth works, couldn’t we just fix all algae problems in a reef tank without the use of chemicals by just dosing nitrates or phosphates like this guy did?

 

[Randy Holmes-Farley]

The Redflied ratio is distorted by reefers into all sorts of incorrect ideas. IMO, all reefers should almost entirely ignore ratios as it is ALWAYS equally good, and usually better, to discuss absolute values of nutrient concentrations.

I do not believe the Redfield ratio says anything useful about nutrients and algae growth, and was never suggested for that purpose by the scientists who invented it.

First, let me describe what the Redfield ratio actually is. It consists of two values that are approximately the same.

1. The first is the N to P ratio in phytoplankton (not anything else). Carbon is also often part of that ratio, but the important implication is that as phytoplankton grows, it must take up N and P in approximately that ratio to build its body tissues.

2. The second is the N to P ratio is seawater itself. There are many contributing chemicals to both, but the total count of n to the total count of P is similar in many parts of the ocean.

What the Redfield ratio DOES NOT say is that any organism needs or prefers N and P in the water to be in that ratio.

Several comments relate to this.

1. The N to P ratio in larger algae forms (say, green hair algae or macroalgae), does not necessarily fit that same ratio, and can vary considerably, so those organisms necessarily take up a something different ratio.

2. Photosynthetic organisms do not prefer nutrients in any specific ratio. What they do prefer (that is, to grow fastest) is to have sufficient N and P and lots of other elements (e.g., manganese, iron) and criteria (light, space, flow, etc.) so that none of these is limiting the growth.

A fundamental principle of growth of an organism such as algae is that it needs a source of N and P to grow. And if that source is low enough in concentration, that limited availability will slow the growth down to match the availability. That is called a limiting nutrient.

If you add more of that nutrient (say, N), then at some increased concentration of N, that organisms will no longer be limited by availability of N, but will become limited by something else. If you increase N still further, there is NO additional boost to growth because something else is in limiting supply. Eventually, of course, if N is incredibly high, it might become toxic in whatever form is present, and begin to slow growth.

It turns out that even in the same ocean water, different algae can have different limitations. For example, some may be limited by N and some by P in the same water.

Thus, the biggest take home lesson for reefers is that:

Algae needs N and P. It needs high enough N and P concentrations in the water to allow uptake for growth. If one or both are present in high enough concentration so that it is not a limiting factor, it makes no difference if there is even more added or not. That addition will not make it grow faster and the ratio does not matter, only the absolute concentration of the limiting nutrient.

Thus, reefers have two ways to look at nutrients and to set nutrient target levels.

1. By ratio. That has the serious problem that it suggests that these three situations with the same ratio are equally suitable, but in fact lead to totally different outcomes:

0.00000001 ppm N and 0.000000001 ppm P
10 ppm N and 1 ppm P
10,000 ppm N and 1,000 ppm P

2. By absolute concentration. Thus, one sets a target or target range, such as 2 to 10 ppm nitrate and 0.03 to 0.1 ppm phosphate, regardless of what ratio is attained while each value is within your target. Obviously one might adjust the target ranges up or down to fit a given scenario, but it is not relying on a ratio alone to set it.

 

[Randy Holmes-Farley]

I'd add that the chart makes no scientific sense, and also does not reflect real reefer experiences.

The yellow area is not a magic "no algae" area.

 

[FrugalReefer]

The Redflied ratio is distorted by reefers into all sorts of incorrect ideas. IMO, all reefers should almost entirely ignore ratios as it is ALWAYS equally good, and usually better, to discuss absolute values of nutrient concentrations.

I do not believe the Redfield ratio says anything useful about nutrients and algae growth, and was never suggested for that purpose by the scientists who invented it.

First, let me describe what the Redfield ratio actually is. It consists of two values that are approximately the same.

1. The first is the N to P ratio in phytoplankton (not anything else). Carbon is also often part of that ratio, but the important implication is that as phytoplankton grows, it must take up N and P in approximately that ratio to build its body tissues.

2. The second is the N to P ratio is seawater itself. There are many contributing chemicals to both, but the total count of n to the total count of P is similar in many parts of the ocean.

What the Redfield ratio DOES NOT say is that any organism needs or prefers N and P in the water to be in that ratio.

Several comments relate to this.

1. The N to P ratio in larger algae forms (say, green hair algae or macroalgae), does not necessarily fit that same ratio, and can vary considerably, so those organisms necessarily take up a something different ratio.

2. Photosynthetic organisms do not prefer nutrients in any specific ratio. What they do prefer (that is, to grow fastest) is to have sufficient N and P and lots of other elements (e.g., manganese, iron) and criteria (light, space, flow, etc.) so that none of these is limiting the growth.

A fundamental principle of growth of an organism such as algae is that it needs a source of N and P to grow. And if that source is low enough in concentration, that limited availability will slow the growth down to match the availability. That is called a limiting nutrient.

If you add more of that nutrient (say, N), then at some increased concentration of N, that organisms will no longer be limited by availability of N, but will become limited by something else. If you increase N still further, there is NO additional boost to growth because something else is in limiting supply. Eventually, of course, if N is incredibly high, it might become toxic in whatever form is present, and begin to slow growth.

It turns out that even in the same ocean water, different algae can have different limitations. For example, some may be limited by N and some by P in the same water.

Thus, the biggest take home lesson for reefers is that:

Algae needs N and P. It needs high enough N and P concentrations in the water to allow uptake for growth. If one or both are present in high enough concentration so that it is not a limiting factor, it makes no difference if there is even more added or not. That addition will not make it grow faster and the ratio does not matter, only the absolute concentration of the limiting nutrient.

Thus, reefers have two ways to look at nutrients and to set nutrient target levels.

1. By ratio. That has the serious problem that it suggests that these three situations with the same ratio are equally suitable, but in fact lead to totally different outcomes:

0.00000001 ppm N and 0.000000001 ppm P
10 ppm N and 1 ppm P
10,000 ppm N and 1,000 ppm P

2. By absolute concentration. Thus, one sets a target or target range, such as 2 to 10 ppm nitrate and 0.03 to 0.1 ppm phosphate, regardless of what ratio is attained while each value is within your target. Obviously one might adjust the target ranges up or down to fit a given scenario, but it is not relying on a ratio alone to set it.

Thanks Randy, a lot of good information. With regards to this talking about Sanjay’s 50 ppm nitrates and 0.50 ppm phosphates.

Sps high nutrients myth?

For some long time reefers have strived to maintain low nutrients levels. Spending hundreds if not thousands of dollars on mechanical, chemical and biological filtration in order to provide corals with a balance of nitrates and phosphates. Many have their own equations on what's best for sps...

www.reef2reef.com

And this talking about Richards 1.24 ppm phosphates.

Skeptical Reefkeeping 9: Test Kits, Chasing Numbers and Phosphate

By Rich Ross and Chris Jury There are many standard parameters in the reefkeeping world that aquarists strive to match in their home reefs – water quality,

reefs.com

Is it safe to say that the reason these thriving tanks have no algae problems is because the coral colonies are large enough that they are outcompeting the nuisance algae for available nutrients

 

[Randy Holmes-Farley]

Is it safe to say that the reason these thriving tanks have no algae problems is because the coral colonies are large enough that they are outcompeting the nuisance algae for available nutrients

I don't know the answer to that, but herbivores and limitation by other ions (e.g., iron or manganese) have been discussed in these scenarios for a long time. Competition for space is also likely another big one. Healthy corals are not good places for algae to grow, and if they cover most surfaces, only the glass remains unprotected.